What we know about the gunman's AR-556 rifle and the modifications you can make to those guns.
Ramon Padilla, USA TODAY

A FBI truck sits in front of the church while investigators worked at the scene of a mass shooting at the First Baptist Church in Sutherland Springs, Tex. The FBI had access to the shooter's cell phone but couldn't access its contents.(Photo: EPA-EFE/LARRY W. SMITH)

SAN FRANCISCO – A simple iPhone passcode may be stopping the FBI from more fully understanding the shooter behind Sunday’s deadly church killing, possibly exacerbated by a gap between when murder suspect Devin Kelley last used the phone and when authorities started trying to unlock it.

The FBI has Kelley’s iPhone, retrieved after he shot a congregation in Sutherland Springs, Tex., killing 25 people before he was killed. A search warrant allowing investigators access has been executed. The phone was flown to FBI headquarters in Quantico, Va., for analysis but so far a forensics team has been unable to unlock the phone.

Their efforts — if prolonged — could resurface a fight between law enforcement, tech companies and privacy advocates over whether the government should get a back-door key to unlocking widely used consumer devices. The FBI has argued it needs to be able to override the phones' encryption to uncover criminals' tracks. Tech companies, including iPhone-maker Apple, have countered doing so would make all individuals more vulnerable to hackers.

Authorities may have had more than one way to get beyond the personal passcode. Versions starting with iPhone 5S and later, but not the new X, use Touch ID. This fingerprint sensor would have allowed the investigators to access the phone using his fingerprints, but only for a short period of time after his last use.

“We are working very hard to get into the phone,” Christopher Combs, the special agent in charge of the FBI’s San Antonio bureau, said during a news briefing on Tuesday. “It could be tomorrow, it could be a week, it could be a month.”

A law enforcement official, who is not authorized to comment publicly, said Wednesday that authorities were still trying to access the contents of the iPhone.

Apple said Wednesday afternoon that no one at the FBI or any other law enforcement agency had reached out to Apple for technical assistance with the phone.

The timing of any such requests is critical.Touch ID allows the owner to set a fingerprint to open the device. However, Touch ID stops working if the phone hasn’t been unlocked for more than 48 hours — at that point the user must type in the passcode, according to Apple’s website. Too many unsuccessful attempts to unlock a passcode can lock down a phone permanently.

If the phone had been set up to accept a fingerprint, the FBI could have used Kelley’s finger to open the phone during that 48 hour window, if he had recently unlocked it. Apple’s Touch ID feature can be engaged with a dead person’s finger.

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Texas Public Safety authorities say the Sutherland Springs church shooting appears to have stemmed from a "domestic situation." It's not the first domestic incident involving suspected gunman Devin Kelley.
USA TODAY

Necessary for crime fighting

Law enforcement officials argue that access to suspects' cell phones is often a crucial component of investigations — but one that's frequently blocked by security technology.

The FBI has been able to retrieve data from fewer than half the mobile phones it has tried to access over the last 11 months, director Christopher Wray said last month at a speech at the International Association of Chiefs of Police conference in Philadelphia.

Manhattan District Attorney Cyrus Vance has warned that inaccessible devices have thwarted some of the office’s most serious investigations, including murder and sex crimes.

Vance is expected to disclose a new count of locked devices later this month. Last year, the district attorney reported that 423 Apple iPhones and iPads had been seized since October 2014 and have been inaccessible to investigators because of default encryption.

“Approximately 10% of our warrant-proof devices pertain to homicide or attempted murder cases, and 9% to sex crimes,” Vance said last year.

“With over 96% of all smartphones worldwide operated by Apple and Google, and with devices running older operating systems rapidly aging out, the trend is only poised to continue,” the district attorney said. “In other words, the risks associated with warrant-proof encryption remain, and are growing.”

Same issues came up in San Bernardino

The issue came to a very public head last year when Apple and the Department of Justice spent 43 days locked in a legal battle over an order from a federal magistrate in California that the company must help the FBI try to get into an iPhone used by San Bernardino gunman Syed Rizwan Farook.

At issue was a feature on the iPhone 5C Farook had been issued by his employer that would lock investigators out if they made 10 unsuccessful tries to determine the correct password.

The FBI demanded that Apple help it disable the locking program, which Apple refused to do on the grounds that creating software to do so would result in something that could potentially unlock any iPhone.

“The FBI may use different words to describe this tool, but make no mistake: Building a version of iOS that bypasses security in this way would undeniably create a backdoor. And while the government may argue that its use would be limited to this case, there is no way to guarantee such control,” Apple CEO Tim Cook wrote in a public blog post on Feb. 16, 2016.

In the end, the FBI paid an estimated $1.3 million to an unnamed company to build a tool that allowed it to break into the phone, and withdrew its case against Apple.

Left unresolved was whether Apple could have been forced to create such a tool for the FBI.

USA TODAY, together with the Associated Press and the news site Vice, sued to discover the name of the outside party that helped crack the phone, but a judge said the agency could keep the identity secret.

Privacy argument

Privacy advocates and civil liberties groups argue that giving police the ability to break into locked phones represents too great a threat to privacy.

Last year the United Nations' human rights chief warned that the creation of cyber tools to do so risked unlocking a Pandora's Box.

"This is not just about one case and one IT company in one country. It will have tremendous ramifications for the future of individuals’ security in a digital world which is increasingly inextricably meshed with the actual world we live in," Zeid Ra’ad Al Hussein, the U.N. High Commissioner for Human Rights, said in a statement in March 2016.

In a show of unity rarely seen in the tech industry, more than 30 companies — Google, Facebook, Microsoft, AT&T, Yahoo, Amazon, Twitter, Intel, Cisco Systems and others — filed amicus briefs in support of Apple in its opposition to cracking an iPhone linked to the San Bernardino killings. It is a formidable front in an industry often fractured by internecine product wars.

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Chairs with roses mark where victims where found in the sanctuary of First Baptist Church in Sutherland Springs. A memorial was created in the sanctuary of the church and opened to the public on Nov. 5, 2017, one week after the attack.
Courtney Sacco, Caller-Times via USA TODAY NETWO

Rachel Vasquez places flowers along the fence surrounding First Baptist Church in Sutherland Springs, Texas on Nov. 12, 2017. One week earlier 25 people and an unborn child were killed in a mass shooting at the First Baptist Church.
Courtney Sacco, Caller-Times via USA TODAY NETWORK

Nearly 300 people congregated in a makeshift church for a closed Sunday service one week after the mass shooting in the First Baptist Church in Sutherland Springs, Texas on Nov. 12, 2017.
R. Tomas Gonzalez, EPA-EFE

Stephen Hope carries a cross in the rain outside the tent near the Sutherland Springs ball park where the First Baptist Church of Sutherland Springs held their first service one week after the shooting that left 25 people and an unborn child dead.
Courtney Sacco, Caller-Times via USA TODAY NETWORK

U.S. Senator John Cornyn, R-TX, and his wife Sandy Cornyn leave their condolences for the victims of the mass shooting in Sutherland Springs' First Baptist Church in Sutherland Springs, Texas on Nov. 12, 2017.
R. Tomas Gonzalez, EPA-EFE

Sam, bottom, and Morgan Stinson, Ohio residents who were vacationing in Texas, leave their condolences for the 26 people who died after a mass shooting in Sutherland Springs' First Baptist Church in Sutherland Springs, Texas on Nov. 12, 2017.
R. Tomas Gonzalez, EPA-EFE

San Antonio resident, Rey Flores kneels near a cross left for a memorial for the people who died after a mass shooting in Sutherland Springs' First Baptist Church in Sutherland Springs, Texas on Nov. 12, 2017.
R. Tomas Gonzalez, EPA-EFE

A tarp is wrapped around the First Baptist Church of Sutherland Springs as law enforcement officials wrap up their investigation into the shooting on Nov. 9, 2017 in Sutherland Springs, Texas.
Scott Olson, Getty Images

Charlene Uhl, right, is comforted as she views a cross with the name and picture of her 16-year-old daughter, Haley Krueger, at a memorial where 26 crosses were placed to honor the 26 victims killed at the First Baptist Church of Sutherland Springs on November 9, 2017 in Sutherland Springs, Texas.
Scott Olson, Getty Images

Police remove a road block as they begin to wrap up their investigation of the shooting at the First Baptist Church of Sutherland Springs on Nov. 9, 2017 in Sutherland Springs, Texas.
Scott Olson, Getty Images

Barbara Solano, center, places flowers at a makeshift memorial for the victims of the First Baptist Church shooting on Nov. 9, 2017, in Sutherland Springs, Texas. A man opened fire inside the church in the small South Texas community on Sunday, killing more than two dozen and injuring others.
David J. Phillip, AP

A police officer nails a Texas Highway Patrol patch to a power pole at a memorial to the 26 victims killed at the First Baptist Church of Sutherland Springs on Nov. 9, 2017 in Sutherland Springs, Texas.
Scott Olson, Getty Images

Joshua John of Roanoke, Virginia prays at a memorial where 26 crosses were placed to honor the 26 victims killed at the First Baptist Church of Sutherland Springs on Nov. 9, 2017 in Sutherland Springs, Texas.
Scott Olson, Getty Images

Vice President Of The United States Mike Pence speaks during a vigil for the Sutherland Springs church shooting of victims at the Floresville high school football field on Nov. 8, 2017.
Courtney Sacco, Caller-Times via USA TODAY NETWORK

Vice President Of The United States Mike Pence speaks during a vigil for the Sutherland Springs church shooting of victims at the Floresville high school football field on Nov. 8, 2017.
Courtney Sacco, Caller-Times via USA TODAY NETWORK

Vice President Mike Pence hugs Evelyn Holcombe at Florseville High School during a stop on Nov. 8, 2017, in Floresville, Texas. A man opened fire inside a church in Sutherland Springs on Sunday, killing and wounding many; Holcombe was in the church during the shooting but escaped.
Eric Gay, AP

Texas Gov. Greg Abbott, in wheelchair, receives a hug from Karen Pence, as he and wife, Cecilia Abbott, welcome Vice President Mike Pence on Nov. 8, 2017, in San Antonio. Pence traveled to Texas to visit victims of the Sutherland Springs First Baptist Church shooting at a local hospital, as well as visit with the families of the victims and participate in a prayer vigil.
Eric Gay, AP

Joshua John Fitch carries a cross past the First Baptist Church which was the scene of the mass shooting that killed 26 people in Sutherland Springs, Texas on Nov. 8, 2017.
Mark Ralston, AFP/Getty Images

Alison Gould ,17 talks about her 16-year-old friend, Haley Krueger, who was killed in the church shooting in Sutherland Springs, Texas. Gould left a stuffed animal at the makeshift memorial near the scene on Nov. 8, 2017.
Courtney Sacco, Caller-Times, via USA TODAY NETWORK

Community members bow their head to pray during a prayer vigil for the victims of the Sutherland Springs First Baptist Church shooting at Floresville high school stadium on Nov. 7, 2017.
Courtney Sacco, Caller-Times via USA TODAY NETWORK

Flags fly at half staff during a memorial service for victims of the mass shooting that killed 26 people in Sutherland Springs, Texas, at the La Vernia High School on Nov. 7, 2017.
Mark Ralston, AFP/Getty Images

A women wipes way tears during a prayer vigil for the victims of the Sutherland Springs First Baptist Church shooting at Floresville high school stadium on Nov. 7, 2017.
Courtney Sacco, Caller-Times via USA TODAY NETWORK

Derrick Bernaden of San Antonio waves burning sage over the 26 crosses honoring those who died in the First Baptist Church shooting in Sutherland Springs, Texas, on Nov. 7, 2017.
Courtney Sacco, Caller-Times via USA TODAY NETWORK

Texas Department of Public Safety Regional Director Freeman Martin, speaks during a press conference near the scene of the shooting at the First Baptist Church Sutherland Springs, TX.
Courtney Sacco, USA TODAY NETWORK

Members of the Sutherland Springs community hold up their cellphones Monday night during a prayer vigil to honor the 26 who where killed in the First Baptist Church shooting, Nov. 6, 2017.
Courtney Sacco, Caller-Times via the USA Today N

Steven Willeford, who has been hailed as a hero for helping to bring down the shooter is embraced by Sutherland Springs community members during a prayer vigil to honor the 26 who where killed in the First Baptist Church shooting, Nov. 6, 2017.
Courtney Sacco, Caller-Times via the USA Today Network

Flowers lay at the road block leading to the First Baptist Church in Sutherland Springs the day after a shooting that multiple people dead, Nov. 6, 2017.
Courtney Sacco, Caller-Times via the USA Today Network

Johnnie Langendorff speaks to reporters about the mass shooting at the First Baptist Church in Sutherland Springs, Texas, on Nov. 6, 2017. Langendorff says he and another man chased down the gunman after he fled the church.
Courtney Sacco, Caller-Times via the USA Today Network

Police officials work in front of the First Baptist Church of Sutherland Springs the day after a mass shooting that left 26 dead, Nov. 6, 2017 in Sutherland Springs, TX.
Casey Jackson, Caller-Times via the USA Today Network

A Texas state trooper stands infront of a closed road leading to First Baptist Church in Sutherland Springs the day after a shooting that left many dead, Nov. 6, 2017.
Courtney Sacco, Caller-Times via the USA Today Network

Mona Rodriguez holds her 12-year-old son, J. Anthony Hernandez, during a candlelight vigil held for the victims of a fatal shooting at the First Baptist Church in Sutherland Springs, Texas, on Nov. 5, 2017.
Nick Wagner/Austin American-Statesman via AP

Wilson County Sheriff Joe Tackett speaks to the media outside the First Baptist Church in Sutherland Springs the day after a shooting that left 26 dead, Nov. 6, 2017.
Courtney Sacco, Caller-Times via the USA Today Network

Texas state troopers stand infant of the closed road leading to First Baptist Church in Sutherland Springs the day after a shooting that left 26 daed, Nov. 6, 2017.
Courtney Sacco, Caller-Times via the USA TODAY Network

Community members gather for a vigil across the street from the First Baptist Church in Sutherland Springs where 26 people where killed in shooting Nov. 5, 2017.
Courtney Sacco, Caller-Times via the USA Today Network

Community members attend a vigil for the victims of a fatal shooting at the First Baptist Church in Sutherland Springs, Texas, on Nov. 5, 2017.
Courtney Sacco/Corpus Christi Caller-Times via USA TODAY NETWORK

Community members gather for a vigil across the street from the First Baptist Church in Sutherland Springs, Texas, where 26 people where killed in shooting on Nov. 5, 2017.
Courtney Sacco/Corpus Christi Caller-Times via USA TODAY NETWORK

Texas Gov. Greg Abbott speaks during a news conference following a shooting that left 26 dead at the First Baptist Church in Sutherland Springs, Texas, on Nov. 5, 2017.
Courtney Sacco/Corpus ChristiCaller-Times via USA TODAY NETWORK

A couple comfort each other at a community center in Sutherland Springs, Texas, near the scene of a mass shooting at the First Baptist Church on Nov. 5, 2017.
Jay Janner/Austin American-Statesman via AP

Carrie Matula embraces a woman after a fatal shooting at the First Baptist Church in Sutherland Springs, Texas, on Nov. 5, 2017. Matula said she heard the shooting from the gas station where she works a block away.
Nick Wagner/Austin American-Statesman via AP

Law enforcement officials stand next to a covered body at the scene of a fatal shooting at the First Baptist Church in Sutherland Springs, Texas, on Nov. 5, 2017.
Nick Wagner/Austin American-Statesman via AP